My company has 2 licenses for Solidworks, one engineer doesn't use his at all so he gave me the discs but he didnt remember where he put the serial number. How do I get another copy of my serial number so I can install and use the software on my computer?

If SOLIDWORKS is already installed on his machine then you can get it under Help > About. Also you will have to transfer the license first from his machine (basically deactivate) and then only you can activate on your machine. Transfer license is also under help menu.